Midnight Humming

This is a strange one, went camping this weekend. Drove 10 miles off road to a sweet spot in the Utah desert. Of course my TRD Pro handled it with ease and no issues. Fast forward 7 hrs, I woke up in my truck tent to a strange humming sound. At first I thought it was a generator from another camper in the distance. When I was fully conscious I realized that wasn’t likely as I was alone for miles and miles. I got out and put my ear to the drivers side bed, just behind the back door. Sure as shit this humming noise was from my truck. I panicked for a brief second as being stranded in the middle of the desert was not how I wanted my weekend to go but the truck fired right up and the sound stopped. All quite the rest of the night and no issue since. Any thought on what this noise was? I’ve speculated a few possibilities like the fuel pump or diff. It was definitely mechanical. Just strange that it happened so long after the truck was shut off.

 

Fuel pump e vap self check.

 

Normal........

 

Search evap self check.....there a a few post about it.